Method of manufacturing endless wood chip webs or the like in an intermittent press



April 21, 1970 K. VAN HLLEN ErAL 3,507,945

METHOD OF MANUFACTURING ENDLESS WOOD CHIP WEBS 0R THE LIKE IN ANINTERMITTENT PRESS Filed Oct. l1, 1968 N .mt

United States Patent O M' U.S. Cl. 264-120 2 Claims ABSTRACT OF THEDISCLOSURE A method of manufacturing endless wood chip webs by advancingintermittently through a plurality of zones, while applying pressure andheat at each zone, a layer of wood chips and binding substance. Thelayer is passed through a pre-pressing zone at room temperature, througha pre-hardening zone at a sharply increased temperature, through a firstcondensation and hardening zone at a continuously increasingtemperature, through an evaporation zone maintained at the increasedtemperature and through a second condensation and hardening zone whichis at a temperature gradually decreasing from the temperature of thefourth zone to room temperature.

BACKGROUND OF THE INVENTION The invention relates to a method ofmanufacturing continuous wood chip webs in an intermittent press fromwood chip eece spread on a conveyor, which corresponds in character tothe desired structure of the web. The present application is acontinuation-in-part of application Ser. No. 507,868, tiled on Nov. 15,1965, and now abandoned.

According to the invention, the wood chips are advanced intermittentlyby the conveyor for a part of its length through the heated press whilebeing sealed through the employment of pressure and heat. It seemsadvantageous to guide the ileece-like material, for example, wood chipiieece, directly before its entrance into the pressing chamber, througha prismatic pre-pressing space which tapers in wedge-shaped form towardsthe pressing chamber.

An undesirable side effect hasv been produced in some instances when theabove method has been carried out in practice.A It seemed indeed, thatthe manufactured endless wood chip web had narrow cross streaks oflesser depth, concentration and firmness than the intermediate webportions, and in addition, was frequently more or less discolored.

The object of the invention is to do away with these streaks. It hasbeen ascertained that the formation of streaks is due to the suddentemperature changes. The steam flowing in the direction of the pressinlet, during the operation of the press, becomes condensed in theregion of the temperature jump and additionally in a limited space, thusleading to damaging cross streaks.

The solution of this problem is effected by doing away with the abrupttemperature changes from 'house temperature at the press inlet to a heattemperature in the press and from the heat temperature in the press toroom temperature and by employing larger so-called condensation zones.

After thorough investigations by the inventors, the formation of streaksin the completed pressed wood chip web could be traced to a collectionof moisture on the corresponding places of the web. It is known that the3,507,945 Patented Apr. 21, 1970 wood chip fleece employed formanufacturing of wood chip web actually contains mechanically orchemically bound moisture which is driven out therefrom to a certaindegree during each sealing and the ensuing vaporization of the partiallength of the wood chip eece in the press chamber. In this case, thesteam escapes sideways from the press i.e. transversely to the directionof movement. A substantial part, however, flows also toward the pressentrance and outlet, therefore in or against the direction of advanceand outlets, therefore in or against the direction of advance. Since inthis case no direct escape is possible, due to the continuous nature ofthe wood chip web, in contrast to the side edges, the steam condenses atthe low temperature zones within the wood chip web at the entrance andoutlet of the press in a tightly limited space.

It has been further discovered that the formation of very narrow zonesof high moisture content, and thus of the above-described damaging crossstreaks, could be avoided with the aid of the below described means, ina simple and certain manner. According to the invention, it is proposedto heat the press in such a manner that the full press temperature ismaintained in an inner, comparatively large zone, i.e. a temperature atwhich the binding substance in the wood chip web will harden and theresulting moisture will evaporate. On both sides of this inner zone, thepress entrance and the press outlet sides, a temperature should bemaintained in the adjacent condensation zones, at which the greater partof" the steam ilowing from the inner zone will be condensed. By thismethod, the condensation in the wood chip web is not restricted to asmall, narrow zone, but is distributed over a greater zone. The lengthof the zone must obviously be so chosen that the corresponding moisturecontent in this zone will not be damaging to the quality of the pressedwood chip web.

In a further development of the invention, there is maintained atemperature in the press, when viewed in the running direction of theweb, in a second zone following the first condensation zone, which issomewhat higher than that of the first condensation zone, but which doesnot reach the full press temperature existing in the inner heating zone.The temperature in the second zone must be sufficiently high, so that nofurther condensation will take place in the second zone. Additionally,the temperature must be so great as to result in a certain bindingbetween the binding substance and the pressed chips.

According to a further feature of the invention, the heating in thepre-hardening zone should be of such a different nature that thetemperatures of the upper and lower press tables, viewed in verticalprojection, rush ahead or after one another and the temperature viewedin the first condensation zone continuously reaches a maximum. Themaximum temperature in the pressed wood chip web then extends along adiagonal plane, following the plane of the splice of the individualpressed lengths of the web. In the region of this diagonal plane, due tothe increased temperature, there is attained a hardening of such extentthat a good union is achieved in the path of the endless wood chip web,because no abrupt break is present between the individual pressedpartial lengths.

It need not be further explained that the transition between theindividual zones, namely the heat zone, the condensation zones and thepre-hardening zone, takes place continuously and not abruptly, which inany case would be hardly possible in production.

The heating of the press must obviously be so arranged that, viewed incross-section of the corresponding wood chip web, no temperaturedifferences will arise along the entire width of the run. This can beeffected by heating the individual zones cross-wise of the conveyorusing, for example, steam heated pipes extending inwardly of the press.The individual pipes of the upper and lower press table are thenadjustably arranged, independent of one another, in order to achieve thedesired temperature circulation in the press. Insulators may preferablybe provided in the individual heating Zones, so that these may beseparated from one another.

The lmethod according to the invention and the device therefor will beillustrated in the accompanying drawing.

In the drawing:

FIG. 1 is a schematic longitudinal section of the press; and

FIG, 2 illustrates diagrammatically a temperature course correspondingin scale to the press of FIG. l.

The press according to the invention comprises a lower stationary press1 and an upper, vertically retractable press table 2. The details of thepress are not shown in the schematic illustration, 4because they are notthe subject of the invention. A conveyor band 3, which may be a sieveband, is guided through the press. Wood chip eece 4 is spread over theband and is sealed in the press under pressure and heat. The chip web isadvanced stepwise into the press, according to the intermittent strokeof the upper press table 2. The position of the wood chip fleece, beforethe pressing and sealing, is indicated by the dotted lines. The chipfleece is led through a prismatic press chamber 7, before it enters thepress chamber 6 proper, said prismatic press chamber being directed likea wedge toward the press chamber. This manner of introducing a chipfleece in a press has proven itself exceptional, particularly in theproduction of endless wood chip webs.

The press had different heating zones. Accordingly, a temperature ismaintained in the first pre-pressing chamber zone which corresponds tothe surrounding room temperature, perhaps increased somewhat by the heatradiation from the press. This zone is indicated by the referencenumeral I. At the junction of this zone I the temperature rises steeplyto a maximum of about 125 C. at the extended curve b, while the curve c,shown in dotted lines, reaches a temperature of only 120 C. The extendedcurve b represents the heating of the upper press table 2, while thedotted line curve c illustrates the heating of the lower press table 1.As may be observed vfrom the path of the curve, the temperature of theupper press table corresponding to the curve b rushes first, ahead ofthe temperature of the lower press table, corresponding to the curve c,viewed in vertical projection. This means that the pressing plate inthis region is heated more intensely by the upper press table 2. Thetemperatures get closer toward the middle of the press and finally reachthe same temperatures at the cross-sectional point of both curves b andc. Thereupon the temperature of the upper press table 2 finally fallsoff faster than that of the lower press table 1. From this point on, thewood chip layer in the press is heated more intensively from below. Ahardened joint is thus obtained, which effects a special binding of thepanel in the transition zones between the individual pressed lengthportions. If the difference in heat were absent, this transition wouldoccur abruptly, each time, in a plane perpendicular to the presentplates plane. It requires no explanation that this would be considerablyworse.

At the junction with the pre-hardening zone II, both of the curves b andc run in about the same direction. They extend from a temperature ofabout 110 C. continuously to the highest temperature of 150 C. Thiszone, indicated as III, forms the so-called first condensation zone. Thesecond condensation zone is indicated as V and is disposed behind aso-called heat zone IV which, as already mentioned, is at 150 C. In thesecond condensation zone V the curves b and c descend again to a lowertemperature. During the pressing of the wood chip web 5, with the pressclosed, an exceptionally large yield of vapor takes place. This vaporcan escape partly sideways at the press; however it also escapes partlyin the direction of arrow d inwardly of the press, Le. toward the pressinlet and outlet. In the heat zones III and IV, this vapor should becondensed over a relatively large vweb length, so that the degree ofmoisture present will be insignificant. Were such a condensation zonenot provided, the condensation atl the press inlet and outlet would berestricted and at the same time the wood chip web would become so wet,that it would be practically unusable. As may be seen from the path ofthe curve, the temperature on both sides of zone IV at first fallsslowly to a lower reading. It is through this quasi-linear fall that agood distribution of the'l condensation over the entire condensationzone is achieved.

It need not be explained further that the heating for each individualzone in the press must be separately controlled to achieve thetemperatures indicated above by wa'y of example. As sho-wn in theschematic drawing of the press, this can be effected by providing hotwater or steam heated channels 8, which are usually constructed as boresin the upper and lower press heating plates. The temperature may beregulated individually in each channel or in groups of channels. Incertain instances individual groups may be constructed as separateelements which are insulated from one another. As shown in the drawing`by the dotted line e, for example, a pair of channels 8 are arranged ineach group.

In the area of the temperature zone IV, the hardening of the chip eecetakes place under pressure and heat. Atthe same time, the concentratedmoisture is driven out of the chip eece in the form of steam. This steamcan escape partly sideways of the press; it ows, however, in the area ofthe temperature zones III and V. Now, there are no substantial drops oftemperature between the zone IV and zone III, but the temperaturegradually falls from C. to 110 C. Therefore, the steam arriving fromzone IV into zone III is not condensed in a tight limited narrow spacetransverse to the feed direction of the band, but, divided in the areaof zone III. At the same time a condensation of the binding meansfollows in the outer panel sheets in the area of zones II and III, whilethe central surface of the panel exhibits at most a slight change of thebinding substance. The reason therefore is that the temperatureprevailing in these zones is less than in zone IV, so that the bindingsubstance can not harden. A precipitate hardening in zone II and zoneIII would result in a loss of quality. In zone I there is only a slightmoisture content which comes out at the zone II, and which isnegligi'bly small. In zone III, Ia complete hardening takes place in thearea bordering on zone IV. This border area will not harden a secondtime, as will be explained further, because a second hardening at thehigh temperature of zone IV would lead to an overhardening of thebinding substance and to a shrinkage of the panels. A part of the steamdriven out of the zone IV ilowsysimultaneously in the area of zone V.Here, too, the temperature does not fall suddenly but slowly, in thelongitudinal direction of the conveyor, to avoid the condensation of thesteam in a tightly limited space.

The portion of the chip panel which was disposed in the area of the zoneII and zone III lies in the last area of zone IV and in the area of zoneV during the above press cycle. Since the binding substance in this areais only confined to a narrow border area by the previous press cycle,there now follows in this area a hardening in the zone IV and in thepart of zone V bordering on zone IV. The travel of the conveyor issynchronized with the length of the press in such a 4manner that thepart of the chip panel which is fully hardened in the border area ofzone III and zone IV lies in the area of zone V, since the temperatureis so low that a second hardening cannot take place.

Summarizing the above, the decreasing temperature in the longitudinaldirection of the conveyor on both sides of zone 'IV serves rstly, thepurpose of providing a relatively large condensation zone for the steamin the longitudinal direction of the conveyor and, secondly, to preventa hardening of the binding substance in the area of the press entranceand -a second hardening of a completely hardened panel in the exit areaof the press. lt should be noted that the pressure over the entireeffective length of the press is the same.

It need not be explained further that the heating of the press isarranged in such a manner, that viewed in the direction of the entirewidth of the web, there are no differences in heating.

We claim:

1. The method of manufacturing endless wood chip Webs in a press, whichcomprise-s: advancing and pressing intermittently through a plurality ofzones of varying temperatures within said press, a layer of wood chipsand binding substance of predetermined width and thickness as follows:first, to a pre-pressing zone increasing from an initial temperature ofC- to 40 C.; second, to a prehardening zone maintained at a temperaturesharply increasing abruptly from 40 C. to 125 C. and decreasinggradually to C., third, through a first condensation and hardening zoneat a temperature increasing gradually to a temperature of C., fourth, toan evaporation zone maintained at a temperature of 150 C., fifth, to asecond condensation and hardening zone wherein the temperature isgradually decreased from 150 C. to 120 C., the evaporation zone beingsubstantially longer than said other zones.

2. The method according to claim 1, wherein said layer passing throughsaid prehardening zone is headed more intensely on the upper surfacethan on the lower surface for 60% of the length of the zone.

References Cited UNITED STATES PATENTS 2,962,459 11/1960 Ash 264-1203,071,805 1/1963 Merkle 264-420 ROBERT F. WHITE, Primary Examiner I. R,HALL, Assistant Examiner U.S. Cl. X.R.

